Consumption of glucose reduces blood flow in the hypothalamus—the part of the brain that controls appetite and hunger—but consumption of fructose does not. Also, fullness and satiety are increased after consuming glucose, but not after consuming fructose.
This was found in a study of young healthy volunteers: 10 men and 10 women of normal weight. The study had a blinded, random order, crossover design, and all participants drank 75 g preparations of pure glucose or fructose. During the next hour, functional magnetic resonance imaging was used to study blood flow in the brain, and a visual analogue scale was used to assess satiety, hunger, and fullness.
Consumption of glucose reduced blood flow in the regions of the brain that control appetite and reward, which in addition to the hypothalamus include the thalamus, insula, anterior cingulate, and striatum. Blood flow was reduced in the thalamus in response to fructose, but also in entirely different regions: the hippocampus, posterior cingulate cortex, fusiform, and visual cortex. Fructose also resulted in lower concentrations of plasma insulin and the satiety hormone glucagon-like polypeptide 1.
Increases in obesity have paralleled the increased consumption of added sugars, including fructose. Although obesity is ultimately caused by excess energy intake, sensations such as hunger and fullness are major determinants of how much people eat (editorial, p 85). Because fructose seems to make people eat more, its intake should be reduced. Sucrose and high fructose corn syrup, which contain about equal amounts of fructose and glucose, are added to sodas, as well as energy and sports drinks. They are also added to juices for small children and many processed foods, including meats and sauces.